This class can to upgrade the convos database from one version to another.

Before running the upgrade,
we try to do a backup of the current redis data related to convos.
If that fail,
we do not continue.

The upgrade is done by fetching the current version that is stored in the database and run the steps from the version after and up to the lastest version available.
Each step is described in the Convos::Upgrader namespace.

It is possible to set the environment variable "CONVOS_FORCE_UPGRADE" if you want to skip the backup step.